1. Field of the Invention
The present invention relates in general to the field of heart monitoring, and more particularly, to devices, methods and systems for determining and outputting in real-time the heart rate, pulse and oxygenation of a patient.
2. Description of Related Art
Pulse and heart rate are both well-known measures to obtain vital statistics of a patient. The pulse can be obtained and pulse rate measured at any location on the body where an artery's pulsation can be transmitted to the surface, typically through pressure. For instance, the pulse may be detected, and pulse rate measured, at locations on the body where an artery can be pressed against bone, including, at the neck (carotid pulse), wrist (radial pulse), finger, hand, foot, etc. At any of these locations, the pulse may be measured by a medical professional pressing their fingers down on the location to feel the pulse and count the number of pulses or beats at such location.
The pulse and pulse rate may also be detected and measured through indirect methods. One such indirect approach is through the measure of light absorption of varying wavelengths in a patient's blood to determine the oxygenation of the patient's hemoglobin. This technique is known as pulse oximetry. Conventional pulse oximetry uses a sensor placed on a thin part of the patient's body, whereby light at red (660 nm) and infrared (940 nm) wavelengths is passed sequentially through the patient to a photodetector. Oxygenation of the blood is measured based upon the ratio of changing absorbance of such red and infrared light through spectral anaylsis. Once measured, both the obtained oxygen level and pulse rate are then displayed on a monitor to the medical professional(s).
Pulse oximetry data is important whenever a patient's oxygenation may be unstable, such as, for instance in intensive care, surgery, emergency and even at birth. However, current pulse oximeters used to detect and measure pulse and pulse rate have a lag time. This lag time extends from the time the pulse oximeter is applied to the patient, to the time a pulse is detected, to the time needed to calculate oxygen level and pulse rate, to the final output of such measures to the medical professional. When time is of the essence, especially at birth when mere seconds are critical to the well-being of the newborn, any such lag time is undesirable. Known pulse oximeters are also influenced by several external conditions including, altitude, temperature, lighting, involuntary movements and nail polish, that affect the accuracy and validity of the readings output by such conventional pulse oximeters. Internal conditions of the patient may also affect the output readings of known pulse oximeters.
Heart rate is another vital statistic, and is often used interchangeably with pulse rate. Heart rate is the number of heartbeats per unit of time, often expressed as beats per minute (i.e., bpm). The heart rate measure may be the same as, or different from, the pulse rate measure.
One approach of obtaining heart rate is by finding a pulse on the patient, counting the pulses or beats, and then calculating the heart rate. For instance, the radial pulse resides at the wrist whereby the radial pulse is felt and measured to obtain a radial pulse rate. Alternatively, the pulse may be detected auditorily and listened-to-beats counted. For an essentially accurate reading, heart rate is obtained by measuring the pulse at a point of maximal impulse (PMI). This type of pulse is referred to as an apical pulse and is generally taken with a stethoscope located on the left side of the chest, about 2 inches to the left from the end of the sternum. As such, an apical heart rate is obtained by taking the pulse over the apex of the heart. An apical heart rate is generally a more accurate and reliable measure of heart rate, as compared to obtaining a heart rate at a location other than at the apex of the heart (e.g., as compared to obtaining a radial pulse/heart rate at the radial bone of the wrist).
In most cases, the apical heart rate will equal heart rates obtained at other locations across the body (i.e., at non-apical pulse locations), and vice versa. However, when the apical heart rate is higher than the non-apical heart rate (e.g. the radial pulse/heart rate), a pulse deficit is observed. This pulse deficit indicates that there is a problem with the blood getting to the arterial point at which such non-apical pulse was taken. Medical attention is often required in such situations. While a pulse deficit may be observed with the apical pulse being lower than the radial pulse, such an occurrence is typically due to human and/or mechanical error.
The heart rate may also be measured using a heart-monitoring device that has a probe positioned over the patient's heart for outputting a heart rate measure to a medical professional. This enables the medical professional to both diagnose and monitor various medical conditions.
One example of a heart-monitoring device is taught in U.S. Pat. No. 6,210,344, issued to Perin, et al., for a method and apparatus for passive heart rate detection. Briefly, this reference teaches a method and apparatus for measuring the heart rate of a patient, which includes a hollow bell mounted on a diaphragm. A transducer element is positioned to receive sound transmitted through the diaphragm, convert the sounds into electrical impulses, and transmit the electrical impulses to a microprocessor. The electrical impulses have real-time wave patterns corresponding to the real-time wave patterns of the original sounds. The microprocessor performs mathematical operations on wave pattern data conveyed by the electrical impulses to determine a numerical value corresponding to the frequency of the wave patterns. This numerical value is sent to a digital output and displayed thereon.
U.S. Pat. No. 5,218,969, issued to Bredesen, et al., discloses an intelligent stethoscope. This intelligent stethoscope is used for performing auscultation and for automatically diagnosing abnormalities based on body sounds wherein the body sounds are received, digitized and stored in memory. The body sounds are recorded from a plurality of locations on the body, and all of the sounds are categorized according to specific characteristics to form a matrix of information. The generated matrix is then compared against a plurality of stored matrices using a technique similar to analysis. Each of the stored matrices contain information indicative of known abnormalities such as specific heart murmurs, lung abnormalities, etc. When a matrix match is found, the diagnosis is displayed on an LCD display formed in the body of the stethoscope. The LCD display is also capable of displaying a visual representation of the recorded body sounds.
Still another prior art reference, U.S. Pat. No. 4,436,096, issued to Dyck, et al., discloses a portable digital heart rate meter/stethoscope. This prior art reference discloses that electrical signals corresponding to heart sounds detected by a pulse/sound transducer are filtered in a narrow band pass filter, whose pass band is centered on a characteristic heart sound frequency of 33 Hz. The filter improves signal-to-noise ratio and enables the transducer to be used over a patient's clothing. The unfiltered signal is amplified and fed to binaural leads to provide the function of an electronic stethoscope. In addition, the filtered signal is converted into pulses in response to which a count corresponding to the detected heart rate is established in a counter and displayed as a digital heart rate indication.
While known mechanical heart rate and pulse monitoring devices are each individually useful after baseline information has been attained, such as those described above, they are not useful when time is of the essence and only a hands-on auscultation is reliable. Furthermore, such known devices do not allow the entire medical team to have a comprehensive awareness of the medical condition of the patient in an immediate and reliable manner. Accordingly, a need continues to exist in the art for improved heart rate and pulse monitoring devices that can be relied on when time is of the essence, and subsequent to such time.